The present application relates to semiconductor devices and, more particularly to a source contact structure and a drain contact structure in fin-based complementary metal oxide semiconductor field effect transistors having unmerged epitaxial source region and an unmerged epitaxial drain region.
As integrated circuits continue to scale downward in size, fin field effect transistors (FinFETs) are becoming increasingly attractive to be used in smaller nodes, e.g., 22 nm node and beyond. Use of multiple fins with an unmerged epitaxial source region and an unmerged epitaxial drain region (hereinafter collectively referred to as “unmerged epitaxial source/drain regions) enables further tailoring of device specification and increased performed. However, with unmerged epitaxial source/drain regions, there is significant loss of contact area since the source contact and the drain contact (hereinafter collectively referred to as source/drain contacts) are typically formed over top portions of the epitaxial source/drain regions and most of the epitaxial source/drain regions are covered by an interlayer dielectric layer (ILD) layer through which the source/drain contacts are formed. The limited contact area can lead to high source/drain contact resistance which in turn degrades device performance. Therefore, there remains a need to improve source/drain contact area for multiple fin FETs with unmerged epitaxial source/drain regions.
Moreover, in a typical process for forming source/drain contacts, contact openings are first etched through the ILD layer and the contact openings are subsequently filled with a metal to form electrical contacts that are in direct contact with the epitaxial source/drain regions. When using an anisotropic etch to form the contact openings, an over-etch is typically performed in order to remove the dielectric material of the ILD layer completely from surfaces of the epitaxial source/drain regions. This over-etch may damage the epitaxial source/drain regions, especially when a silicon germanium alloy (i.e., SiGe) with a high Ge content is employed to form the epitaxial source/drain regions. Therefore, there remains a need to protect the epitaxial source/drain regions during the etch process in forming the source/drain contact openings.